This invention relates to welding the ends of metal strips together for feed to a continuous forming mill such as a mill for making welded steel pipe or for sheet rolling.
It is common to operate metal forming and similar operations on a continuous basis. For example, steel strip is uncoiled and fed continuously into a pipe mill to produce completed pipe. In such a mill, heavy steel rolls curl the strip of steel around its length to form a closed tube. The longitudinal seam is continuously welded by electrical resistance welding or arc welding to close the pipe. The completed pipe is then cut to convenient lengths. Other forming or coating operations may also be conducted on a continuous basis, commencing with metal strip. For example, the strip may be cold reduced to a desired thickness and/or slit to a desired width, tin plated, galvanized or painted.
The raw material for a continuous mill is ordinarily in the form of a coiled strip which is uncoiled into a "looper", the output of which goes into the forming mill. The length of strip in the looper is sufficient that strip can be continuously withdrawn from the looper into the mill while the input to the looper is stopped for connecting the front of another strip to the tail of a strip that has already entered the looper. A splicing station is provided between the coil and the looper for making such a connection.
A typical splicing station includes a shear for trimming the tail of one strip and the front of the next strip so that they match. Downstream from the shear is a welding station, which may be mounted on a movable carriage for drawing the ends of the two strips together for welding. Downstream from the welding station, that is between the carriage and the looper, there is typically a pair of pinch rolls for gripping the tail of the strip that has already entered the looper.
Side guides are provided for the edges of the strip, and these are typically moved transversely to the sheet length to bring the edges of the two strips into alignment. This may cause damage to the edges of the strips, such as bending or buckling, or upsetting a thickened portion along the edge.
When the strips are properly aligned, the two ends are butt welded together. In conventional practice, this leaves a bead of weld metal at the seam running transverse to the strips. When the welded seam has passed through the looper and passes through the mill, the thick seam of weld metal, and in some cases the battered edges of the strips near the seam, batter the forming rolls. This damages the surface of the rolls and eventually leads to sufficient damage that the rolls must be replaced and reground to produce the desired quality of pipe or strip from the mill.
Thus, it is desirable to minimize damage to the rolls and other structures of the forming mill so that premature replacement is not required. Whatever is done to avoid such damage must be accomplished without interrupting the continuous operation of the mill. In other words, it must be done quickly.